Ultrasonic Flow Measurement Used in HVAC Technology
Time:2023-01-03 Read:301
Reading guide: As we all know, HVAC technology and flow measurement technology are inseparable. The ultrasonic flowmeter can adapt to different pipe diameters and various media. The ultrasonic sensor is installed outside the pipe, which has no impact on the flow of media in the pipe and can ensure the personal safety of workers and the safety of the production process.

What is HVAC technology?

First, HVAC stands for heating, ventilation and air conditioning. The system provides heating and cooling for residential and commercial buildings. We can find HVAC technology anywhere, from single family homes to submarines, which provide a means of environmental comfort. More and more popular in new buildings, these technologies use fresh air from outside to provide high indoor air quality. V in HVAC, namely ventilation, is the process of replacing or exchanging air in a space. This provides better indoor air quality, including the removal of moisture, smoke, odor, heat, dust, airborne bacteria, carbon dioxide and other gases, as well as temperature control and oxygen replenishment.

Heating, ventilation, and air conditioning engineering is an indispensable component in the field of capital construction

Saving energy, protecting the environment, ensuring working conditions, and improving the quality of life all play very important roles. HVAC systems continue to consume energy during the operation of buildings. How to reduce energy consumption through rational system selection and optimal design plays a huge role in achieving the goal of building energy conservation and promoting the development of green buildings.

HVAC technology

How does HVAC technology work?

The three main functions of HVAC technology are interrelated, especially when providing acceptable indoor air quality and thermal comfort. Heating and air conditioning technology is usually one of the most complex and extensive technologies in the home, but when it stops working, we will soon know! HVAC system has nine parts. We should be familiar with air return, filter, exhaust port, pipe, electrical components, outdoor unit, compressor, coil and blower. The technology of each part is closely related to air flow measurement, water flow measurement, pressure measurement and temperature measurement.

Trends in the heating, ventilation and air conditioning (HVAC) industry

According to the investigation and report of Statista Research Department, heating, ventilation and air conditioning (HVAC) technology provides environmental comfort through thermal operation (heating and air conditioning) and acceptable indoor air quality (ventilation). Sometimes refrigeration is also included in the field of HVACR. The HVAC industry is largely driven by regional regulations and differences: it is said that Asia is one of the regions with the largest HVAC market, and the demand for air conditioning is greater than other regions. At the same time, Italy is one of the largest European countries in the heat pump market in 2020. Due to these differences between countries, there is little or no comparative information about this competitive market. For example, in the United States alone, a degree of fragmentation can be observed, as the number of employees in the plumbing and HVAC industry varies from state to state.

heating, ventilation and air conditioning (HVAC) industry

Measurement of air conditioning water flow by ultrasonic flow measurement technology

At present, an ultrasonic flowmeter is the most simple, convenient, and safe method for measuring air conditioning water flow. The ultrasonic flowmeter has a wide range of applications and is easy to install. It can adapt to different pipe diameters and various media. The ultrasonic sensor is installed outside the pipe, which has no impact on the flow of media in the pipe and can ensure the personal safety of workers and the safety of the production process.

Composition and working principle of ultrasonic flowmeter:

The ultrasonic flowmeter is composed of a host (with keyboard, display, and micro printer), an externally bound standard M-type sensor (also called a probe), a power cord, and a connecting line between the host and the sensor. SUP-2000H portable ultrasonic flowmeter uses a built-in rechargeable nickel metal hydride battery, which can work for about 20 hours after being fully charged.

The measurement principle is the principle of ultrasonic propagation time difference. The time difference formula is used to measure the velocity by the time difference method, that is, the propagation time of the sound wave at a certain velocity changes between the two sensors due to the fluid flow. The fluid velocity can be obtained by measuring this relative change, and the fluid flow can be obtained by inputting the pipe size.

Operation steps and technical points to be noted for measuring air conditioning water flow with an ultrasonic flowmeter:

1. Enter parameters.

Open the machine and input the parameters of the tested object, including pipe outer diameter, pipe wall thickness (measured with ultrasonic thickness gauge), pipe material, lining material parameters (if any, lining thickness and lining material sound velocity), fluid type, probe type (because the host can support a variety of different probes), and probe installation mode. After inputting the above parameters, the probe installation distance according to the above probe installation method will be displayed. Then the operator shall install the probe according to the above installation method and the installation distance of the sensor probe.

2. According to the actual situation on site, correctly select and determine the location of the air conditioning water flow measuring point

The installation of an ultrasonic flowmeter is the simplest and most convenient among all flowmeters. Just select a suitable measuring point, input the pipe parameters at the measuring point into the flowmeter, and then install the probe on the pipe. When selecting the measuring point, it is required to select the part with a smooth and uniform fluid distribution. In order to ensure measurement accuracy, the following principles should generally be followed:

2.1 Select the pipe segment filled with fluid, such as the vertical part of the pipe or the horizontal pipe segment filled with fluid.

2.2 The measuring point shall be a straight pipe section that is more than 10 times the diameter from the upstream and more than 5 times the diameter from the downstream (note: the distance required by different instruments will be different, and the specific distance shall be subject to the instrument manual), without any uniform valves, elbows, tees, reducers, and other interference.

2.3 Ensure that the temperature at the measuring point is within the working range (the working environment temperature range of the flowmeter host is - 10 ℃~70 ℃, and the working temperature range of the sensor probe is - 30 ℃~150 ℃. Contact the manufacturer if the temperature range is exceeded).

2.4 Fully consider the scaling condition on the inner wall of the pipe, and try to select the pipe section without scaling for measurement. If it can not be satisfied, it is necessary to consider scaling as lining for better measurement accuracy

2.5 Select pipe sections with uniform and dense pipes and easy ultrasonic transmission.

3. Wiring between the sensor probe and host.

The probe of the portable ultrasonic sensor adopts different colors to distinguish the upstream and downstream probes, which are simple and clear, easy to connect and operate.

4. Correctly select the installation method of the sensor probe.

There are four ways to install sensors. They are called the V method, Z method, N method, and W method respectively. The following are respectively described. Generally, the V method can be selected for small pipe diameters (DN100-300mm); If the V method fails to measure the signal or the signal quality is poor, the Z method shall be selected. When the pipe diameter is more than DN300mm or when measuring the cast iron pipe, the Z method shall be preferred. N method and W method are less used and suitable for fine pipes below DN50.

4.1 V method: V method is generally a standard installation method, which is convenient to use and accurate in measurement. The measurable pipe diameter ranges from 25 mm to about 400 mm; When installing the probe, the center line shall be horizontal with the pipeline axis.

4.2 Z method: when the installation signal of the V method is weak and the machine cannot work normally due to the thick pipeline or the presence of suspended solids in the liquid, the scaling on the inner wall of the pipe is too thick or the lining is too thick, Z method shall be used for installation. Because this method is used for installation, the ultrasonic wave is transmitted directly in the pipeline without refraction (called single path), and the signal attenuation is small. The measurable pipe diameter ranges from 100mm to about 6000mm. In the actual installation, it is recommended that the Z method should be used for pipes above 300mm.

4.3 N method: it is not commonly used. During installation, the ultrasonic beam refracts twice in the pipeline and passes through the fluid three times (three sound paths), which is suitable for measuring small-diameter pipelines. This method improves the measurement accuracy by extending the ultrasonic transmission distance.

4.4 W method: it is a very uncommon method. As with the N method, the measurement accuracy of the small tube is improved by extending the ultrasonic transmission distance. Suitable for measuring small tubes less than 50mm. Using the W method, the ultrasonic beam refracts three times in the pipe and passes through the fluid four times (four sound paths).
5 Mount the sensor probe.

Before installing the probe, clean the area outside the tube where the probe is to be installed, remove all rust and paint, and select the dense part of the tube for probe installation. Apply enough couplant on the central part of the probe and the pipe wall, and then press to firmly attach the probe to the pipe wall.

6 Check the installation.

Observe the signal strength, signal quality, total transmission time, time difference, and transmission time ratio displayed by the flowmeter to determine whether the installation is optimal. If it is not good, slightly adjust the probe position until these parameter values reach the range specified in the instrument manual. If it cannot be adjusted, it is necessary to change the proper installation method. After the sensor position is adjusted, fix the sensor.

7 Re confirm that the signal strength, signal quality, signal transmission time difference, transmission time ratio and other parameter values meet the specified requirements, and then read the actual flow value from the host display panel.

Measurement of air conditioning water flow by ultrasonic flow measurement technology

Technical measures to ensure the accuracy of measurement results:

1. The input pipe parameters must be correct first, otherwise, the whole flowmeter cannot work normally. Correct input of pipeline parameters is the key to ensuring accurate measurement results. The accuracy of the instrument itself is obtained under the correct pipe parameters, but the operator is required to input the correct pipe parameters during measurement to obtain the correct flow value. Pipe diameter error and pipe wall thickness measurement error have a great influence on measurement accuracy.

2. The measuring point position and sensor installation mode shall be correctly selected to ensure the normal and stable operation of the ultrasonic flowmeter.

3. Make sure that the measured water pipe is full of pipe flow. The ultrasonic flowmeter actually measures the velocity of the fluid. The flow is calculated according to the input pipe diameter and then multiplied by the flow rate. Only full pipe flow can ensure that the test data is accurate.

4. Make preparations, and the pipe surface treatment at the measuring point shall be in place. The pipe can be polished to bright and smooth without corrosion pit by using tools such as an angle grinder, file, and sandpaper. The paint rust layer is required to be polished, and the protrusions shall be smoothed to avoid local depressions, with uniform luster and a smooth and round feel. Special attention shall be paid to that the polishing point shall have the same radian as the original pipe, and the mounting point shall not be polished into a plane.

5. The installation of the sensor probe is directly related to the accuracy of the flow value and the long-term reliable operation of the machine. In most cases, the probe is simply coated with a coupling agent and pasted outside the pipe wall to obtain the measurement results. At this time, the signal strength, signal quality, total transmission time, time difference, and transmission time ratio should be checked. During sensor installation, enough coupling agents shall be used to paste the sensor probe on the pipe wall. Make sure there is no air bubble and sand between the sensor and the pipe wall to ensure good coupling.

6. On the horizontal pipe section, two probes shall be installed in the horizontal direction of the pipe axis, and within ± 45 ° of the horizontal position of the axis, to prevent the normal measurement from being affected by the phenomenon of insufficient fluid in the upper part of the pipe, bubbles or sediment in the lower part.

7. The sensor installation and pipe wall reflection must avoid the interface, weld, or flange installation.

8. As a precision instrument, the ultrasonic flowmeter will cause certain errors in measurement if it is used for a long time. It should be sent to the legal measurement unit for verification according to the specified period, and a correction factor should be provided to reduce the measurement error.

9. During daily use or transportation, handle with care to avoid damage.

10. The pipe diameter error, sensor installation error, and pipe wall thickness measurement error have a great impact on the measurement accuracy of the ultrasonic flowmeter, but they can be controlled through accurate measurement and strict installation. Therefore, the operators must be skilled, operate correctly, and improve their operating skills to ensure accurate measurement results. During installation, it is recommended that the Z method should be used for all pipes above 300mm.